Estimated glomerular filtration rate among intensive care unit survivors: From the removal of race coefficient to cystatin C-based equations

Abstract

Purpose: Black race coefficient used in serum creatinine (sCr)-based estimated glomerular filtration rate (eGFR) calculation may perpetuate racial disparities. Among intensive care unit (ICU) survivors, sCr overestimates kidney function due to sarcopenia. Cystatin C (cysC) is a race- and muscle mass-independent eGFR marker. We investigated the impact of removing the race coefficient from sCr-based eGFR and compared cysC- and sCr-based eGFR in ICU survivors.

Materials and methods: Among 30,920 patients from 2 institutions in the Bronx and Boston, eGFR was calculated at hospital discharge using sCr-based equations with and without race coefficient (eGFRsCr₂₀₀₉ and eGFRsCr₂₀₂₁). In a subset with available cysC between ICU admission and 1-year follow-up, sCr- and cysC-based estimates were compared.

Results: eGFRsCr₂₀₂₁ was higher than eGFRsCr₂₀₀₉ by a median of 4 ml/min/1.73 m² among non-Black patients and lower by a median of 8 ml/min/1.73 m² among Black patients. Removing race coefficient reclassified 12.9% of non-Black subjects and 16.1% of Black subjects to better and worse eGFR category, respectively, and differentially impacted the prevalence of kidney dysfunction between the institutions due to differences in racial composition. Among 51 patients with available cysC (108 measurements), cysC-based estimates were lower than sCr-based estimates (median difference 9 to 16 ml/min/1.73 m²), resulting in reclassification to worse eGFR category in 34% to 53.5% of measurements.

Conclusions: Among ICU survivors, removal of race coefficient leads to lower eGFR in Black patients and may contribute to overestimation of kidney function in non-Black patients. While cysC is rarely used, estimates based on this marker are significantly lower than those based on sCr.

Keywords: Critical illness; Cystatin C; Estimated glomerular filtration rate; Intensive care unit.